Obesity has become a worldwide epidemic and causes serious public health problems. Now about one third of adults and approximately 17% of children and adolescents aged 2-19 years are obese in the United States. Obesity has been linked to life-threatening diseases such as type 2 diabetes and cardiovascular disease. Our strategies for tackling obesity epidemic are largely inadequate. Theoretically, obesity could be controlled by increasing energy expenditure and controlling diet, but the success rates with these approaches remain poor. A better understanding of the control of energy balance will facilitate our capability for overcoming this problem. Growing data from this and other labs have underscored specific roles for the dorsomedial hypothalamus (DMH) in the controls of both food intake and energy expenditure. The overall goal of this research project is to more comprehensively unravel the neural bases of these actions. We have found that overexpression of orexigenic neuropeptide Y (NPY) in the DMH causes hyperphagia and obesity, whereas DMH NPY knockdown results in decreased food intake, brown adipocyte development in white fat, increases in brown fat thermogenesis and body energy expenditure, and weight loss. These findings establish critical roles for DMH NPY in the controls of food intake and energy expenditure, but the underlying neural pathways remain undetermined. This project is aimed at elaborating such pathways by the following two Specific Aims. In Aim 1, we propose experiments to characterize the neural pathways underlying the feeding effects of DMH NPY by assessing whether: (1) DMH NPY descending signals modulate the activity of brainstem neurons innervated by vagal afferents to control food intake, and (2), DMH NPY innervates anorexigenic neurons (such as oxytocin) in the paraventricular nucleus to modulate food intake. Experiments proposed in Aim 2 are to ascertain the neural mechanisms underlying the thermogenic effects of DMH NPY. We will first determine the importance of DMH NPY in thermoregulation and characterize the underlying neuronal signaling. Given the presence of corticotrophin-releasing factor (CRF)-expressing neurons in the thermogenic area of the DMH, the second part of Aim 2 is to assess whether DMH CRF mediates DMH NPY modulation of thermogenesis and to evaluate a potential thermogenic function of DMH CRF. We will apply multiple approaches including an adeno-associated virus system to alter NPY and CRF expression in the DMH, pharmacological and physiological interventions of gastrointestinal signaling, neuroanatomical analyses using c-Fos as a neuronal activation marker and green fluorescent protein and cholera nontoxic B subunit for tracing neuronal projections, interfering neural signaling with central microinjections of receptor-specific antagonists or agonists, diet or cold challenges, and evaluating neural signaling at both gene and protein levels, to achieve these Aims. Overall, the results from this project will not only significantly advance our understanding of the central control of energy balance, but also provide the neural bases for the development of novel strategies for combatting obesity and its comorbidities.